Front-End callbacks are sequences in the FrontEndCallbacks.seq file multiple user interface applications can call to share the same implementation for a specific operation. The FrontEndCallback.seq file TestStand installs in the <TestStand>\Components\Callbacks\FrontEnd directory contains one LoginLogout Front-End callback. The TestStand Sequence Editor and default user interfaces call the LoginLogout callback.

Use Front-End callbacks to implement operations so you can modify a Front-End callback without modifying the source code for the user interfaces or rebuilding the executables for the user interfaces. For example, to change how various user interfaces perform the login procedure, modify only the LoginLogout sequence in FrontEndCallbacks.seq.

To modify the default implementation of the Front-End callback or to create new Front-End callbacks, copy the FrontEndCallbacks.seq file from the <TestStand>\Components\Callbacks\FrontEnd directory to the <TestStand Public>\Components\Callbacks\FrontEnd directory and make any changes to the copy of the file. You can use functions in the TestStand API to invoke the modified Front-End callback from each user interface application you create. However, because you cannot edit the source for the sequence editor, you cannot make the sequence editor call new Front-End callbacks you create.